This invention relates to a three-phase slotted armature winding wherein coils are laid in stator core slots such that a winding in each pole of each phase has a concentric double-layer winding arrangement.
In the following description, a winding comprises a coil or a plurality of series coils laid in slots for forming each pole and each coil comprises a plurality of turns of an electrical wire. A winding forming a pole is referred to as a pole winding.
A lap winding and a concentric winding are known as coil arrangements in a three-phase armature winding. In the lap winding, coils having the same configuration and coil pitch are placed one upon the other in sequence and laid in the slots. Electric characteristics of each phase are advantageously balanced since the coils have the same configuration and the winding resistance and leakage reactance of each phase are equal. However, the coil inserting work cannot be automatized since the coils of different phases are placed one upon the other into double-layers and laid in one and the same slot, resulting in a disadvantage that the work needs to be manually performed by workers.
On the other hand, in the concentric winding, a plurality of coils different in the coil pitch in a winding of each pole of each phase are laid in the slots so that the coils are distributed so as to be concentric about the pole center. The coils can be laid in the slots by a coil inserting machine generally called automatic coil inserter and the inserter has been widely used for its superior productivity.
Japanese Published (kokoku) Patent Application No. 47-42881 discloses a double-layer lap type armature winding which has a coil arrangement wherein the automatic coil insertion can be performed at every one pole winding by the automatic coil inserter. In this case a coil transposing work is eliminated wherein a coil side of the initially laid winding is taken out of the slot when a final winding is laid in the slot, and coil sides of the final and initial windings are laid in the empty slot with the coil side of the initial winding placed on that of the final winding. However, in the case of the three-phase four-pole arrangement, for example, the coil inserting operation need to be performed at twelve times, which number corresponds to the number of poles.
Japanese Published (kokoku) Patent Application No. 48-24284 discloses an armature winding of the concentric double-layer type. The same number of times of the coil inserting operation as in the above-described armature winding is required in the case of the three-phase four-pole arrangement and additionally, the troublesome coil transposing work is also required.
Japanese Published (kokoku) Patent Application No. 51-28125 discloses an armature winding of the concentric single-layer type armature winding, in which the coil inserting operation need to be performed only at four times in the case of the three-phase four-pole arrangement but an amount of copper used is disadvantageously increased as will be described with reference to FIG. 44.
FIG. 44 illustrates a conventional three-phase four-pole armature winding of the concentric single-layer type. Coils are laid in the slots in the order of all poles of phase U, those of phase V and those of phase W at every phase. Accordingly, end windings are disposed in the order of the phases U, V and W inwardly from the outer circumferential side and the pole coils are positioned in four ranges of approximately 90 degrees respectively obtained by equally dividing an annular area surrounding the rotor. In FIG. 44, first to fourth poles are represented as U1 to U4 with respect to the coils of phase U, respectively and those poles of the phases V and W are represented as V1 to V4 and W1 to W4 in the same manner as described above with respect to the phases V and W, respectively. The arrangement shown in FIG. 44 results in the following problems:
First, since the armature winding is a single-layer winding wherein a single coil is laid in each slot, the coil insertability is reduced in the case of the type with a large coil volume and it becomes difficult to shape the end windings after the insertion. Consequently, the coil surface is damaged or an axial dimension of the coil needs to be increased for avoidance of difficulty in shaping. Accordingly, the thickness of each slot insulator or interphase insulator needs to be sufficiently increased so that the winding is durable sufficiently in the end winding shaping step.
Second, the dimension of the end winding differs from phase to phase since the end winding of each phase is arranged such that the different phases are radially arranged. Accordingly, since differences in the winding resistance and leakage reactance unbalance the winding impedances of the respective phases, resulting in various electrical deficiencies such as unbalance in the excitation current. Additionally, when the core dimensions are the same as in the lap winding type, the concentric type is inferior in various electrical characteristics to the lap type and an amount of copper used is larger.